De novo purine biosynthesis, a primary metabolic process, was recently found to differ in vertebrates and fungi. The key step involves the carboxylation of AIR (5-aminoimidazole ribonucleotide) to CAIR, 4- carboxyl-5-aminoimidazole ribonucleotide. In the fungal system, two enzymes, PurK and PurE, are required to produce CAIR while the vertebrate system requires only AIR carboxylase. More importantly, the fungal pathway proceeds through a short-lived intermediate, N/5-cair (5- carboxyaminoimidazole ribonucleotide), in the formation of CAIR. Based on these significant differences in enzyme reactivity, it may be feasible to synthesize a inhibitor that would act selectively with the fungal enzymes. The goal of this research training proposal is to design a library of potential inhibitors of the fungal enzymes, PurK and PurE, by solid- supported chemistry using a variation of combinatorial chemistry called array chemistry. The parallel array will consist of 36 compounds synthesized simultaneously but separately. The compounds synthesized in the array are analogs of 5-aminopyrazole ribonucleotide (APR). Three areas of diversity have been outlined to maximize the structural differences of the library. Once synthesized, the compounds will be tested in several enzymes and anti-fungal screens.